Toner cartridges for laser printers are well known in the art. Generally, a cartridge will include sufficient toner for a large number of “typical” prints, such as 10,000 or 25,000, packaged in a housing which also contains those printing components that require periodic replacement, such as a photosensitive drum, magnetic and charging rollers, a “doctor” blade and a cleaning blade. The printing components and housing typically have a usable life, if properly cleaned and maintained, that greatly exceeds the number of prints for which toner is provided. Hence, toner cartridges are often remanufactured with a new supply of toner.
Remanufactured toner cartridges are both cost effective for consumers and environmentally sound. Original Equipment Manufacturers (OEMs) of printing equipment often provide “recycling” programs that allow consumers to return empty toner cartridges; the returned cartridges are shredded to recover some of the raw materials. Remanufacturing, in contrast, directly reuses most of the components of the cartridges, thereby greatly reducing the amount of material ending up in landfills, and having a substantially smaller “carbon footprint” than “recycling”.
In a typical laser printer, a revolving photosensitive drum or belt having a surface capable of holding a localized static charge is “charged” to a uniform voltage; a modulated laser is then scanned across the surface to remove the charge from those areas which are intended to be blank in the final image. A layer of toner, in the form of a fine powder, is then applied to the belt or drum by a “doctor blade”; the toner adheres to those areas of the belt or drum that have retained a charge. The drum or belt then deposits the toner on a print medium (such as paper), and residual toner is wiped off the drum or belt by a “cleaning blade.”
In early generations of laser printers, the initial charge on the belt or drum was provided by corona wires. Newer printers typically use a roller mechanism, usually called the Primary Charge Roller (PCR) to charge the drum. The shift from corona wires to PCRs helped alleviate several problems associated with early laser printers, including high ozone emissions and “corona” streaks on prints attributed to the wires.
The PCR is generally a small diameter roller made of a compliant material, and having an outer surface adapted to transfer an electrostatic charge to the photosensitive drum. The PCR is generally held against the drum or belt, with the movement of the drum or belt causing to PCR to rotate. Typically, the primary charge roller is charged with both an alternating current signal, which functions to remove any residual or “ghost” static charges on the drum left from previous images, and a direct current bias, which functions to charge the surface of the drum or belt to a uniform voltage. The amplitude of the uniform direct current bias voltage to a large extent determines the darkness of the final prints.
The PCR typically has a conductive metal shaft, with each end of the shaft resting in a “saddle” which is configured to hold the PCR against the photosensitive drum, typically using springs. At least one of the saddles is formed of a conductive material, through which electrical contact with the PCR is provided. In some cartridges, a bare section of shaft exists at each end of the PCR adjacent to the saddle, as will be evident in the discussion below. Although replacement parts are generally readily available in the cartridge remanufacturing industry, it is common practice for cartridge remanufacturers to clean and reuse the cartridge's original PCR roller.
A challenge faced by toner cartridge remanufacturers is variability among components available for use in remanufactured cartridges. Components may be of varying ages, minor engineering changes may have been made between production runs of a cartridge, or it may be necessary to use a combination of refurbished parts and new replacement parts.
The toner used in a remanufactured cartridge can also vary from that used by the OEM. While the remanufacturer will typically specify a toner that essentially matches the important performance characteristics of the OEM toner, and therefore provides a print quality close to the OEM toner, toner formulations are complex, involving many production steps and constituents. Some aspects of the OEM toner may be covered by patents, or different toner additives may be used due to availability or cost.
The OEM has the ability to “fine tune” the printing system, including the components in the cartridge, the toner, and the operation of the printer itself, including various initialization and cleaning operations. The OEM may, for example, formulate the materials of the photosensitive drum, the cleaning blade, and PCR such that the printing system functions reliably for the number of prints provided by the original supply of toner, but not necessarily for the extended life of a refilled cartridge. The OEM may also utilize coatings or treatments on the components which are substantially degraded due to wear by the end of the original “life” of the cartridge.
The wear on components and differences in toner formulations may result in prints produced over time with a remanufactured cartridge exhibiting print defects. For example, prints may begin to show a gray background haze. Investigations have shown one cause of the haze to be a polymeric residue that forms on the PCR, apparently from toner additives, such as wax and cleaning agents.
Repeating defects may also appear which occur on the printed page at a frequency corresponding to the circumference of the PCR. These defects can be caused by small residual amounts of toner that are not removed from the photosensitive drum by the cleaning blade, and which are subsequently deposited on the PCR. Small spots of toner thus form on the PCR roller, which are compressed each time the spot contacts the photosensitive drum, rendering the spots essentially permanent. Since the portion of the drum contacted by the spot will not be properly charged, the resulting prints will show a recurring dark spot running down the page.
Some OEM laser printer cartridges include PCR cleaning mechanisms, although in cartridges intended for a single use this may consist only of a simple strip of film which contacts the PCR roller. Experience with remanufactured cartridges show that a basic PCR cleaner of this nature is relatively ineffective in preventing the kind of print defects often observed with remanufactured cartridges. Also known in the art are more complex PCR cleaning mechanisms, such as felt rollers, as shown, for example, in Japanese Laid-Open Patent Publication No. JP2272589 (“Image Forming Device”, inventors Tanaka Hisami and Hirayama Noriko, applicant Canon KK, published 1990 Nov. 7).
To keep the cost of remanufactured cartridges low, it is important that any modifications to the cartridge be done in a manner that requires as few steps as possible and that don't require significant changes to the cartridge itself.
There is thus a need for remanufactured toner cartridges which do not exhibit print defects attributable to PCR roller contamination, and for methods allowing simple retrofitting of cartridges.